NEFL and tropical spastic paraparesis: As Nf-L in plasma in this cohort of patients with HAM correlates not only with the levels of Nf-L in CSF but also with the CSF concentrations of inflammatory markers, it may be an alternative to monitor disease activity in patients with HTLV and to detect early, subclinical neuronal damage in those considered asymptomatic carriers of HTLV-1 infection.